1. Field of the Invention
The present invention relates to a shift mechanism as well as a vehicle and a motorcycle including the shift mechanism, and particularly, to a transmission apparatus, a shift mechanism, and a vehicle including the shift mechanism used in an Automated Manual Transmission (AMT) apparatus.
2. Description of the Related Art
An example of a known transmission mechanism of a motorcycle includes an electronic control transmission, or so-called AMT, with automated clutch operation and automatic control of shift operation based on Manual Transmission (MT). In the AMT, manipulation of a shift switch by hand indicates a shift-up or a shift-down of multistage transmission gears and an actuator of a transmission is driven according to the indication to automatically perform the shift change operation (changing a gear stage in a transmission apparatus).
To change the gear stage in the AMT, the actuator drives a shift mechanism in the MT to intermittently turn a shift cam through the shift mechanism. The intermittent turning of the shift cam moves a shift fork in a gear shaft direction of the transmission along a groove provided on the periphery of the shift cam to rearrange the gear dog by a tip of the shift fork to change the gear to a predetermined gear stage.
Particularly, in the shift operation in the MT of a motorcycle, the rider operates a shift pedal (also called a change pedal) by foot to vertically move the shift pedal to input an operation to the shift mechanism. In this type of shift mechanism, a first speed gear stage is set as a gear stage corresponding to an end of the operation in the shift-down direction. This is to prevent the traveling posture of the vehicle from becoming unstable after involuntary loss of driving force as the gear stage of the transmission apparatus is switched to neutral when an excessive operation in the shift-down direction is accidentally performed. Specifically, a neutral position is set between a first speed gear position and a second speed gear position in the turning angle of the shift cam, and the first speed gear position is set at the end on the lower gear side. In this manner, the gear positions in the turning angle of the shift cam are set in the order of first speed, neutral, second speed, third speed, . . . , and sixth speed (top gear), from the end on the lowest gear side in the shift mechanism. This will be called a bottom-low shift pattern.
In a motorcycle of the MT including the shift mechanism of the bottom-low shift pattern, the rider performs the shift change by substantially the same operation in the operations of the shift-up from first speed to second speed, from second speed to third speed, and in other shift-up operations. Similarly, the rider performs the shift change by substantially the same operation in the shift-down from second speed to first speed, third speed to second speed, and in other shift-down operations.
Therefore, in a shift cam used for the bottom-low shift mechanism, the phase angle between the first speed gear position and the second speed gear position is set substantially at the same angle as the phase angle between the second speed gear position and the third speed gear position or the phase angle between other adjacent gear positions. In this manner, the rider performs the operation without particularly recognizing the gear change between the first speed and the second speed from the gear change between other gear positions.
In the shift mechanism including the bottom-low shift pattern, the neutral position in the shift cam is provided in the phase substantially at the center between the first speed gear position and the second speed gear position. As a result, the turning angle of the shift cam from the first speed gear position to the neutral position or from the second speed gear position to the neutral position is substantially one-half (½) of the turning angle of the shift cam between the second speed gear position and the third speed gear position or in other shift changes.
In other words, when the motorcycle of the MT including the bottom-low shift mechanism is driven, the amount of operation (turning angle of the shift cam) in the operation of switching the gear to neutral (shift change from the first speed gear position to the neutral position or from the second speed gear position to the neutral position) is substantially one-half of the shift change between other gear stages, and the position easily moves to the second speed or first speed gear position beyond the neutral position. Therefore, the rider needs to cautiously and slowly operate the shift pedal (input section of the operation drive in the transmission mechanism of MT) and be careful not to turn the shift cam too much.
Meanwhile, it is desirable in the AMT to set constant feed angles of the shift cam for each stage transmission, i.e., angles defined by cam phase holding portions of the index cam between any gear stages including the neutral position. This is because the AMT is configured to perform shift change operations by driving the shift mechanism by the actuator and intermittently turning the shift cam through an intermittent turn mechanism, and the drive and control of the actuator, the rotation and braking of the shift cam, and holding of the phase are simplified. Furthermore, this sets a constant time and stabilizes the time required by the AMT for the shift change in order to provide a transmission operation that the rider can rely on.
In the AMT, the gear stage currently set in the shift mechanism and used for the drive in the transmission mechanism is determined from information of a sensor or the like used in the vehicle, and traveling of the vehicle is further determined to perform an interlock control in which the gear stage of the transmission mechanism is not switched to neutral during traveling or the like. The interlock control prevents the traveling posture of the vehicle from becoming unstable after an involuntary loss of the driving force as the gear stage is switched to neutral when the rider accidentally performs an excessive operation in the shift-down direction without using the mechanical bottom-low system in the shift mechanism.
Therefore, in the AMT, the neutral position is mechanically set at the end on the lowest gear side in the shift mechanism, and first speed, second speed, . . . , and sixth speed (top gear) are sequentially set from there to the neutral position at the end of the low gear side. This will be called a bottom-neutral shift pattern. Therefore, in the shift cam used for the shift mechanism including the bottom-neutral shift pattern, the rotation angle set between the neutral position and the first speed gear position is substantially the same angle as the rotation angle between the first speed gear position and the second speed gear position or between other adjacent gear positions.
An example of a structure that holds the shift cam at a predetermined phase includes a transmission apparatus disclosed in Japanese Patent Application Laid-Open No. 6-123355. In Japanese Patent Application Laid-Open No. 6-123355, concave portions corresponding to gear stages are provided on a peripheral cam surface of an index cam at predetermined intervals in the circumferential direction, and a follower (positioning roller) abuts and presses against the cam surface including the concave portions. Through the operation in Japanese Patent Application Laid-Open No. 6-123355, the phase of the index cam and the shift cam linked together is converged to and engaged with the concave portions of the cam surface. In Japanese Patent Application Laid-Open No. 6-123355, the shift cam is rotated by input of an operation, and the follower is engaged with the concave portions provided at predetermined intervals (phase angles). This achieves one gear stage change (shift cam feed), in which the feed angle (angle defined by cam phase holding portions of index cam) in intermittent turns of the shift cam is a predetermined angle.
The shift mechanism of Japanese Patent Application Laid-Open No. 6-123355 is a shift mechanism including the bottom-low shift pattern described above. More specifically, among the concave portions provided on the periphery of the index cam at intervals in the circumferential direction in the shift mechanism, the concave portion corresponding to the neutral position (neutral concave portion) is provided at the center phase between predetermined concave portions (concave portion corresponding to the first speed gear position and concave portion corresponding to the second speed gear position).
In the AMT, there is a demand to control transmission gears with six or more stages in the shift mechanism including the bottom-neutral shift pattern, instead of the bottom-low shift mechanism.
As described above, the AMT is configured to rotate the shift cam by a predetermined angle to perform the gear shift. When the AMT includes a bottom-neutral shift mechanism corresponding to a six-stage transmission, the peripheral cam surface of the index cam includes seven concave portions (index positions) in total at equal intervals, including six concave portions corresponding to gear positions of six stages and one concave portion corresponding to neutral. In this case, seven portions are provided at equal intervals on the peripheral cam surface of the index cam to define the concave portions.
Meanwhile, the feed angle of one intermittent turn of the shift cam through the index cam is smaller than the feed angle (e.g., 60 degrees) of one intermittent turn in a six-speed MT including the bottom-low shift mechanism. Therefore, the following problem occurs if the outer diameter (diameter) of the shift cam and the distance of the movement of the shift fork in the gear shaft direction in the engagement of the dog of each transmission gear are the same as those of the six-speed MT including the bottom-low shift mechanism. More specifically, the lead angle of the groove to move the shift fork provided on the peripheral surface of the shift cam in the gear shaft direction in the AMT is an angle that is more acute than in the shift cam used in the bottom-low six-speed MT. Therefore, when the bottom-neutral shift mechanism corresponding to the six-stage transmission is applied to the AMT, the torque to be provided to the shift cam needs to be increased to quickly rotate the shift cam in the transmission.